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Old 19th April 2013, 04:38 AM   #1
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Default Switching Noise Between Preamps

I use two preamps.

I have a high quality selector to choose which pre I'm listening to.

I feed a single source to the selector and then use the selector to choose which pre.

If both preamps are on there is a pop when switching.

If only one pre is on, no pop when switching.

If both preamps are off - no pop when switching.

What's up?
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Old 19th April 2013, 09:09 AM   #2
DF96 is offline DF96  England
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DC level changes. One or both preamps probably lacks a ground resistor at the input or output (on the outboard side of the coupling capacitor).
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Old 19th April 2013, 12:34 PM   #3
AndrewT is offline AndrewT  Scotland
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Those grounding resistors can be of very high resistance value.
When the interconnects are in place and the source is selected/active, the very high resistance has a virtually zero effect on proper circuit operation.
I habitually use 2M2 at the output and input of all my interconnected equipment.
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Old 19th April 2013, 12:58 PM   #4
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Quote:
Originally Posted by bassnkeys View Post
I have a high quality selector to choose which pre I'm listening to.

I feed a single source to the selector and then use the selector to choose which pre.
Just so I understand you: you mean to feed a single source to both preamps and then select the output of the preamp you want to listen to?

jan
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Old 19th April 2013, 03:18 PM   #5
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jan.didden,
You are correct... I was not clear.
I am taking the output from a DAC that has two sets of outs.
One set of outs to each pre.
Each pre always has signal available.
Source to DAC.
DAC to each pre.
Pre 1 to A and Pre 2 to B of an A/B switch.
Output from A/B switch to power amp.

Last edited by bassnkeys; 19th April 2013 at 03:21 PM.
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Old 19th April 2013, 03:54 PM   #6
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Also, one pre is actually a B1 buffer built from the Pass board.
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Old 19th April 2013, 04:01 PM   #7
AndrewT is offline AndrewT  Scotland
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The B1 has a DC blocking cap on the output.
Have you fitted a ground referencing resistor after that cap?
What about the output of the other pre?
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Old 19th April 2013, 04:45 PM   #8
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I have not made any additions to the Pass design.
I am going to open the other pre this afternoon for a look.
30f and 6" of new snow in central MN.
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